A symphony is an extended musical composition in Western classical music, scored almost always for orchestra.

A symphony usually contains at least one movement or episode composed according to the sonata principle.

Many symphonies are tonal works in four movements with the first in sonata form, which is often described by music theorists as the structure of a "classical" symphony, although many symphonies by the acknowledged classical masters of the form, Joseph Haydn, Wolfgang Amadeus Mozart, and Ludwig van Beethoven do not conform to this model.